1. Field of the Invention
The present invention elates to a method for fabricating a connection device of a highly integrated semiconductor device, and more particularly to a semiconductor connection device capable of reducing the total a ea of connection portions by minimizing an overlap area between a lower first conduction line and an upper second conduction line at a contact region defined in the first conduction line upon connecting the second conduction line to the first conduction line.
2. Description of the Prior Art
In general fabrication of a semiconductor device, a contact hole is formed in an inter-layer insulating film formed over a first conduction line by etching the insulating film so as to electrically connect a second conduction line to the first conduction line through the insulating film. A second conduction layer is deposited and then patterned to form the second conduction line. The second conduction line is electrically connected to the first conduction line through the contact hole. Upon forming the second conduction line, the contact hole is fully overlapped with the second conduction line because of the reason to be described hereinafter. For forming the second conduction line to be overlapped with the first conduction line, the above-mentioned patterning step is carried out subject to a condition that the first conduction line is overlapped with a mask which is preferably comprised of a photoresist film. If the mask covers the contact hole incompletely, the first conduction line may be damaged at the portion disposed beneath the uncovered portion of the contact hole during the patterning of the second conduction line. As a result, poor semiconductor devices may be produced.
Therefore, masks for forming the contact hole and the conduction line should be designed in accordance with a specific regulation.
In other words, the mask to be used for forming the contact hole for connecting the second conduction line to the first conduction line and the mask to be used for forming the second conduction line should be designed such that the mask for the second conduction line is always overlapped with the contact hole. When the mask for the second conduction line covers the contact hole incompletely, the first conduction line may be partially etched through the contact hole during the patterning of the second conduction line, so that the first conduction line may have a damaged portion. Where the mask for the second conduction line has the same size as the contact hole, it may cover the contact hole incompletely due to a limitation on accuracy and a variation in critical dimension encountered in fabrication of masks, and a misalignment, a distortion of lenses and a variation in critical dimension occurring upon formation of a pattern on a wafer. As a result, the first conduction line may have a damaged portion, as mentioned above. Taking the above-mentioned parameters into consideration, the mask for the second conduction line is formed to have a size larger than that of the contact hole by a predetermined dimension so that it can cover the contact hole completely. However, this results in an increased dimension of a connection device finally produced.
FIG. 1 is a plan view of a connection device in accordance with the prior art. As shown in FIG. 1, the conventional connection device has a structure wherein each second conduction line C is connected to a corresponding first connection line A through a contact hole B. It is noted that this structure has an increased connection area because of the size of the second conduction line overlapped with the contact hole B. In other words, the second conduction line C has an increased area for overlapping with the contact hole B, thereby increasing the connection area.
FIG. 2 illustrates another conventional structure wherein each second conduction line C is insufficiently overlapped with the corresponding contact hole B so that the connection area can be considerably reduced. Even though this structure has a greatly reduced connection area, misalignment of the conduction lines occurs. In other words, the second conduction line C may be misaligned with the contact hole B, so that the contact hole B has a portion not covered with the second conduction line C. This means that the first conduction line A may be damaged due to the uncovered contact hole portion upon formation of the second conduction line C.
FIGS. 3A to 3C are sectional views taken along the line a-a' of FIG. 2, respectively illustrating a method of forming a connection device resulting in the above-mentioned structure wherein the second conduction line C is insufficiently overlapped with the contact hole B.
In accordance with this method, an inter-device isolation insulating film 2 and a first conduction line 3 comprised of impurity-diffused regions are formed on predetermined portions of a semiconductor substrate 1, respectively, as shown in FIG. 3A. Over the entire exposed surface of the resulting structure, an inter-layer insulating film 4 is formed. Thereafter, a contact hole 10 is formed in the insulating film 4 so that the first conduction line 3 is exposed through the contact hole 10.
As shown in FIG. 3B, a conduction material layer 5 for a second conduction line is then formed over the entire exposed surface of the resulting structure so that it is in contact with the contact hole 10. Subsequently, a mask 6 for the second conduction line is formed on the conduction material layer 5. FIG. 3B shows a condition that the mask 6 covers the contact hole 10 insufficiently. Such a condition is results from a misalignment and a variation in critical dimension occurring in formation of the mask 6.
FIG. 3C shows second conduction lines 5' formed by etching predetermined portions of the conduction material layer 5 by use of the mask 6 shown in FIG. 3B. By referring to FIG. 3C, it can be found that the first conduction line 3 has been etched through the contact hole portion not overlapped with the mask 6, thereby forming a damaged portion 20. The damaged portion 20 resulting from the etching of the first conduction line 3 penetrates the substrate 1, thereby resulting in a poor semiconductor device.
For preventing such a damaged portion from being formed in fabrication of a connection device, the mask 6 for the second conduction line is constructed to cover the contact hole 10 completely in accordance with the conventional method. However, such a structure causes a problem that the connection area is naturally increased because the second conduction line still remaining after a subsequent etching step extends beyond the boundary of the contact hole.